This invention relates to a recording medium on which digital data, such as compressed moving-picture video data, sub-video data, or audio data, has been recorded, a reproducing device for reproducing the recording medium, a data reproducing device for reproducing the data, and a data reproducing method, and more particularly to those capable of automatically controlling the reproducing condition to the best one.
As everyone knows, optical disks have been widely used in the form of compact disks (CDs) for music only or laser disks (LDs) compatible with moving-picture video.
Recently, a system has been developed which compresses moving-picture video data, audio data, and sub-video data (e.g., subtitle data) and records them with a high density. It records speech and subtitles in more than one language in advance and selects and reproduces the speech and subtitles of the desired language during reproduction. An optical disk compatible with this type of system is generally known as a DVD.
Various types of optical disks have been available. A reproducing device for reproducing such an optical disk comprises a rotary servo unit for controlling the rotation of an optical disk and an optical pickup for reading the modulated signal recorded on the optical disk by projecting a laser beam onto the signal recording surface of the optical disk and sensing the reflected light.
The signal read by the optical pickup is input to a waveform equalizer circuit, which subjects the signal to a waveform equalizing process. The waveform-equalized signal is supplied to an error correction circuit, which subjects the signal to an error correcting process. The error-corrected signal is then directed to a demodulation circuit, which demodulates the signal.
In a conventional optical disk reproducing device, the waveform equalizer circuit has a fixed characteristic. The reason is that the optical disk and the reproducing device for reproducing it are supposed to have one-to-one correspondence.
Actually, there are many types of optical disks as described above. Therefore, when an optical disk different from the expected compatible optical disk is loaded into the optical disk reproducing device and the optical disk is reproduced, the characteristic of the modulated signal obtained from the optical pickup may be very different from the characteristic of the signal to be reproduced by the reproducing device. In this case, the user may mistakenly believe that the optical disk is out of order or the optical disk is defective.
Furthermore, even when the optical disk is of the same standard, various parameters do not necessarily fulfill the standard ideally because optical disks differ from manufacturer to manufacturer or the characteristic of the optical disk reproducing device changes with time. As a result, there may be a case where an optical disk reproducing device cannot obtain an ideal modulated signal. In this case, the probability of data errors is high, making it impossible to produce a good reproduced signal.